Middle aged people who smoke, have high blood pressure or diabetes are far more likely to develop dementia in later life, suggests research published ahead of print in the Journal of Neurology, Neurosurgery and Psychiatry.

People should consider modifying their lifestyle in mid-life to avoid developing dementia, claims the US research.

Dementia is a growing public health problem affecting older people in developed countries. In the US, where the research took place, estimates show that one in six people older than 70 have dementia. Estimates are that the number of people with dementia will grow threefold by 2050, compared with 2000.

Previous studies have shown that the presence of cardiovascular risk factors including high blood pressure, diabetes, obesity and smoking increase the risk of developing subsequent dementia, but have often failed to show the relationship.

Researchers from the universities of Minnesota, North Carolina and John Hopkins and the University of Mississippi Medical Center studied more than 11,000 people aged 46-70 who were participants in the Atherosclerosis Risk in Communities (ARIC) study in 1990-92.

People underwent a physical examination and cognitive testing at that time and they were followed up until 2004 to see how many were hospitalised with dementia.

After following their progress, the researchers identified 203 cases of hospitalisation with dementia. Smoking, high blood pressure and diabetes were all strongly associated with dementia in white participants and African-Americans.

The results showed that rates of hospitalisation with dementia increased exponentially with age in men and women and in different ethnic backgrounds.

Overall, African-Americans had a two and a half times higher rate of hospitalisation than white people and African-American women in particular had the highest rates of all.

Current smokers were 70% more likely than those who had never smoked to develop dementia, people with high blood pressure were 60% more likely than those without high blood pressure, and people with diabetes were more than twice as likely than those without diabetes to develop it.

No association was found between people who were obese/overweight and dementia in later life.
The authors say the results suggest that smoking cessation and prevention or control of high blood pressure and diabetes starting in midlife may have the added benefit of decreasing dementia hospitalisation risk.

They conclude: "Our results emphasise the importance of early lifestyle modification and risk factor treatment to prevent dementia."